Nonwoven fabrics are useful for a wide variety of applications, including absorbent personal care products, garments, medical applications, and cleaning applications. Nonwoven personal care products include infant care items such as diapers, child care items such as training pants, feminine care items such as sanitary napkins, and adult care items such as incontinence products. Nonwoven garments include protective workwear and medical apparel such as surgical gowns. Other nonwoven medical applications include nonwoven wound dressings and surgical dressings. Cleaning applications for nonwovens include towels and wipes. Still other uses of nonwoven fabrics are well known. The foregoing list is not considered exhaustive.
Various properties of nonwoven fabrics determine the suitability of nonwoven fabrics for different applications. Nonwoven fabrics can be engineered to have different combinations of properties to suit different needs. Variable properties of nonwoven fabrics include liquid handling properties such as wettability, distribution, and absorbency, strength properties such as tensile strength and tear strength, softness properties, durability properties such as abrasion resistance, and aesthetic properties.
The manufacture of nonwoven fabrics is a highly developed art. Generally, nonwoven webs and their manufacture involve forming filaments or fibers and depositing the filaments or fibers in such a manner so as to cause the filaments or fibers to overlap or entangle. Depending on the degree of web integrity desired, the filaments or fibers of the web may then be bonded by means such as an adhesive, the application of heat or pressure, or both, sonic bonding techniques, or hydroentangling, or the like. There are several methods within this general description; however, one commonly used process is known as spunbonding and resulting nonwoven fabric is known as spunbond fabric.
Generally described, the process for making spunbond nonwoven fabric includes extruding thermoplastic material through a spinneret and drawing the extruded material into filaments with a stream of high velocity air to form a random web on a collecting surface. Such a method is referred to as meltspinning. Spunbond processes are generally defined in numerous patents including, for example, U.S. Pat. No. 4,692,618 to Dorschner, et al.; U.S. Pat. No. 4,340,563 Appel, et al.; U.S. Pat. No. 3,338,992 to Kinney; U.S. Pat. No. 3,341,394 to Kinney; U.S. Pat. No. 3,502,538 to Levy; U.S. Pat. No. 3,502,763 to Hartmann; U.S. Pat. No. 3,909,009 to Hartmann; U.S. Pat. No. 3,542,615 to Dobo et al.; and Canadian Patent 803,714 to Harmon.
Other methods of making nonwoven fabrics involve the formation of fibrous webs with staple fibers. As used herein, polymeric fibers and filaments are referred to generically as polymeric strands. Filaments means continuous strands of material and fibers means cut or discontinuous strands having a definite length. Staple fibers may be formed into entangled webs by conventional processes such as carding, airlaying, or the like.
Although nonwoven fabric properties such as liquid handling properties, strength properties, softness properties and durability properties, are normally of primary importance in designing nonwoven fabrics, the appearance and feel of nonwoven fabrics are often critical to the success of a nonwoven fabric product. The appearance and feel of nonwoven fabrics is particularly important for nonwoven fabrics which form exposed portions of products. For example, it is often desirable that the outer covers of nonwoven fabric products have a cloth-like feel and a pleasing decorative design.
Outer covers of personal care products typically function as a liquid barrier and normally include a solid film of thermoplastic material such as polyethylene film rather than a nonwoven fabric. As a result, such materials often have a firm, smooth outer surface whereas it is more desirable that such materials have a more cloth-like feel.
One method of applying a decorative design to nonwoven products is by printing a decorative design on the outer cover with ink. However, printing does not alter the feel of the material. Embossing is one method to alter the feel of nonwoven fabrics and add a decorative design. Different methods for embossing nonwoven fabrics and films are known. Some bonding methods are designed primarily to affect the strength properties of the fabric and are not capable of imparting a particularly decorative design to the fabric. One such example is a method disclosed in U.S. Pat. No. 4,592,943 to Cancian et al. In that method, a nonwoven web is heated as the web passes between two grids so that the grids impart a pattern of rectangular densified areas to the web. Although this method is effective to alter the strength properties of the fabric, its use in applying a decorative pattern to fabric is limited because the possible designs of the grids are limited. A more versatile method of embossing nonwoven fabrics and films is pattern roll embossing. For example, U.S. Pat. No. 4,774,124 to Shimalla et al. discloses a method wherein a pair of pattern embossing rollers are used to emboss nonwoven fabric.
Despite the advances in the art described above, there is still a need for improved patterned nonwoven webs and methods of their manufacture. In particular, there is a need for liquid barrier outer cover materials with improved appearance and feel and improved methods for making such materials.